Fishing lines based on ultrahigh molecular weight, high tenacity, polyolefin yarns represented a dramatic shift in the technology of fishing lines. The filaments and their manufacturing process are described in Kavesh et al. U.S. Pat. No. 4,413,110; Smith et al. U.S. Pat. No. 4,344,908; Smith et al. 4,422,993; Kavesh et al. U.S. Pat. No. 4,356,138; Maurer E. P. 55,001; Harpell et al. U.S. Pat. No. 4,455,273; Kavesh et al, U.S. Pat. No. 4,897,902; Neal U.S. Pat. No. 5,277,858; and Kirkland et al. WO 94/00627. In general, the filaments are made by spinning from a gel solution containing the polymer in a solvent. As the solvent is removed from the spun filament, the filament is stretched to form a high strength, high tenacity filament of high molecular weight. Filaments made from linear polyethylene or polypropylene exhibit a molecular weight of at least 400,000, a tenacity of at least 15 g/denier, a tensile modulus of at least 500 g/denier, a melting point of at least 140° C.
Once bundled into yarns, a plurality of yarns can be made into an excellent fishing line. Processes for doing so are described in Cook U.S. Pat. Nos. 5,749,214; 5,540,990 and 6,148,597. The process described in these patents generally teach a re-stretching or “re-drawing” process under suitable heat and tension to cause the fishing line to lengthen with an increase in tenacity.
Another process is described in Cunningham et al. U.S. Pat. No. 5,573,850 which discloses a yarn having a polyethylene core that is then sheathed in a heated polymeric coating. The result of this process is described as providing monofilament-like characteristics to a multifilament construction.
The disclosures of each of these patents are herein incorporated by reference.
The high tenacity and low degree of stretch while submerged in water has made such fishing lines an important tool for anglers of all skill levels. Despite their technological prowess for many aspects of fishing, however, lines made from ultrahigh molecular weight, high tenacity polyolefin yarns have one shortcoming for some anglers: the lines float. With a specific gravity of only 0.97, some fishing techniques require that the fishing line have a negative buoyancy to get the lure at the right depth with the right action at that depth.
The use of weights added to the terminal end of the line do not satisfactorily address the issues associated with a floating line. For example, floating lines tend to pull a trolled lure to the water's surface thereby requiring additional weight to pull the lure back down. This combination of factors postures the lure in an upward orientation or with a more sharply sloping angle to the trailing line than would be desired. Floating lines may also disrupt or prevent a fishing technique that relies on a nonmoving lure that might stimulate a stunned prey.
It would be desirable to have a fishing line with the high tenacity and low stretch properties that are characteristic of fishing lines made with ultrahigh molecular weight, high tenacity, polyolefin yarns but with an overall specific gravity of greater than 1.0 so that the fishing line has negative buoyancy apart from any added weight, terminal connector or lure. This is not as easy as one might think.
A fishing line should have a relatively smooth exterior surface along its entire length. Such smoothness dramatically affects the drag resistance characteristics of the fishing line so surface bumps, ridges and protrusions above the line surface are defects that should be avoided to make a desirable fishing line. Thus, any composite of fishing line yarns must consider the yarn accumulation process, e.g., braiding, twisting or nonwoven formation, as well as the processing temperature, duration, draw rate (if any), number of draw stations and the chemistries associated with any processing aids, lubricants, coatings or the like that are used during the manufacturing process. All of the materials used in any composite must act in substantially the same way, despite any differences in chemistry, to minimize or avoid surface protrusions immediately following manufacture as well as up to months after manufacture despite a wide variety of packaging, shipping and storage conditions and extremes.
It would further be desirable to have a sinking, composite fishing line that would have a minimum of surface defects despite extended storage conditions and environmental extremes.